The results they're looking at, however, may be based on a race to get the early shoppers.

If there are a significant number of people who are going to do their shopping the minute the sale opens, but are not going to buy extra just because the sale lasts longer: then the store that opens a bit ahead of the others will get those particular sales. The result of this is that every store (or, in this case, every mall) tries to open the sale a bit ahead of all the others; which may well result in their all staying open extra hours, at considerable extra cost, without any of this increasing total sales a bit. The customers buy the same amount that they would anyway; they just do it, each year, a few hours earlier.

ETA: do you suppose that, eventually, they'll back up the big annual sale all the way to the day after Christmas, landing us right back where we were (if my memory doesn't fail me) around the late 1950's? except, of course, for the bit about everybody being open 24/7/365.

But the way that markets work is that if it isn't worth it, a company will stop doing it, and gain a competitive advantage by not wasting money on it. Then others will follow suit. So it may keep backing up some, but if it isn't worth it, the market should (eventually) find the point where it is just worth it from an economic perspective.

I would guess we're getting close to that point or have slightly overshot, but I could be wrong.